1. Field of the Invention
The present invention relates to a method and system of relaying calls and, more particularly, to a tone provision function in the next generation mobile communication network.
2. Background of the Related Art
‘ITU-T Q.1901 BICC’ is a protocol for the next generation core network that allows Narrow-Band Integrated Services Digital Network (ISDN) User Part (ISUP) call processing function, supporting the Narrow-Band ISDN services recommended in ‘ITU-T Q.761–769’, to be applied in packet-based networks, such as an Asynchronous Transfer Mode (ATM) network or an Internet Protocol (IP) network, regardless of the bearer technology or the signaling message transport method.
FIG. 1 illustrates a configuration of a related communication network that relays calls between gateway controllers using the ITU-T Q.1901 Bearer Independent Call Control (BICC) protocol. The communication network includes two gateway controllers 11 and 14 and two wireless gateways 12 and 15. The information transmission between the gateway controllers 11 and 14 and the wireless gateways 12 and 15 is conducted through the IP-based core network 13, using IP. The protocol stack between the gateway controllers 11 and 14 includes BICC, IP, and Transfer Control Protocol (TCP) or ATM. On the other hand, the protocol stack between the gateway controllers 11 and 14 and the wireless gateways 12 and 15 includes Media Gateway Control Protocol (MGCP), 3rd Generation-Inter-Operability Service (3G-IOS), IS-41D, IP, and TCP or ATM.
Furthermore, the gateway controllers 11 and 14 employ MGCP to control resources of the wireless gateways 12 and 15, and the BICC protocol is used to support the relay calls between the gateway controllers 11 and 14.
The related art method of relaying calls in the next generation mobile communication network is illustrated in FIG. 2. Initially, the originating wireless gateway 12 transmits a service request message (3G-IOS_CM_Service_Request) to the originating gateway controller 11, wherein the service request message (3G-IOS_CM_Service_Request) is a message announcing a call attempt from a mobile device. The originating gateway controller 11 confirms the service request message (3G-IOS_CM_Service_Request) and transmits a resource assignment request message (3G-IOS_Assignment_Request) to the originating wireless gateway 12, requesting assignment of a radio channel.
The originating wireless gateway 12 receives the resource assignment request message (3G-IOS_Assignment_Request) and transmits a response message (3G-IOS-Assignment_Complete) to the originating gateway controller 11. The originating gateway controller 11 transmits a connection instruction message (MGCP_CRCX) to the originating wireless gateway 12, requesting a resource assignment for the connection with the core network 13. An available radio channel can be selected at the side of the base station and TCP/IP ports are opened at the side of the originating wireless gateway 12, in response to the connection instruction message. In this manner, the resource assignment for the core network connection is requested and confirmed. Then, the originating wireless gateway 12 transmits a response message (MGCP_CRCX_Ack), including the information on the assigned core network connection (i.e., the core network IP address and IP port number, bandwidth information, etc.), to the originating gateway controller 11.
Subsequently, the originating gateway controller 11 transmits an Initial Address Message (IAM; BICC_IAM), including information on the call receiver, the caller, and other information regarding the core network connection of the originating wireless gateway 12, etc., to the terminating gateway controller 14 in order to request a BICC call connection.
The terminating gateway controller 14 executes 3G-IOS paging procedures to send paging request messages (3G-IOS_Paging_Request) to the wireless gateways under its management, wherein the paging request message (3G-IOS_Paging_Request) is used to identify the terminating wireless gateway 15 presently connected with the call receiver. Then, the terminating wireless gateway 15, currently connected to the call receiver, transmits the paging response message (3G-IOS_Paging_Response) to identify itself to the terminating gateway controller 14. Thereafter, the terminating gateway controller 14 transmits the resource assignment request message (3G-IOS_Assignment_Request) to the terminating wireless gateway 15, and the terminating wireless gateway 15 returns a response message (3G-IOS_Assignment_Complete) to the terminating gateway controller 14.
The terminating gateway controller 14 requests and confirms the resource assignment, for the connection, with the core network 13, by transmitting the core network IP address and IP port information, bandwidth information, etc., of the originating wireless gateway 12. This information is received by the terminating gateway controller 14 in the IAM (BICC_IAM). The terminating gateway controller 14 transmits this information to the terminating wireless gateway 15 through the connection instruction message (MGCP_CRCX). The terminating wireless gateway 15 then transmits a response message (MGCP_CRCX_Ack) and an alert message (3G-IOS_Alert) to the terminating gateway controller 14 to inform it that the call receiver is being called.
Thereafter, the terminating gateway controller 14 transmits an Address Complete Message (ACM) (BICC_ACM) to the originating gateway controller 11, informing it that the call receiver is being called. The ACM is a return message informing the originating gateway controller 11 that all of the address information required to identify the call receiver has been received.
After the terminating wireless gateway 15 transmits a connect message (3G-IOS_Connect) to the terminating gateway controller 14, informing it that the call receiver answered the call, the terminating gateway controller 14 transmits an Answer Message (ANM) (BICC_ANM) to the originating gateway controller 11. The ANM is another return message informing the originating gateway controller 11 that the call receiver answered the call. The ANM initiates the imposition of a service charge, if the connected call is a domestic call, or starts measuring the communication time, for the calculation of an international call service charge, if the connected call is an international call.
Thereafter, the terminating gateway controller 14 requests and confirms the resource assignment for the connection with the core network 13, by transmitting the connection instruction message (MGCP_CRCX) to the terminating wireless gateway 15. The MGCP_CRCX message requests the resource assignment, for the terminating wireless gateway's connection with the core network, to establish voice communication between subscribers. The terminating wireless gateway 15 transmits an acknowledgment message (MGCP_CRCX_Ack), including information on the assigned core network connection, to the terminating gateway controller 14.
The terminating gateway controller 14 then transmits an Application Transport Mechanism (APM) message (BICC_APM) to the originating gateway controller 11, containing information on the core network connection of the wireless gateway 15. This information includes the core network IP address and IP port number, bandwidth information, etc.
Accordingly, the originating gateway controller 11 transmits a modification connection message (MGCP_MDCX), to transfer information regarding the core network connection of the terminating wireless gateway 15, to the originating wireless gateway 12 and receives an acknowledgment message (MGCP_MDCX_Ack) from the originating wireless gateway 12 in return. Then, the originating gateway controller 11 responds to the terminating gateway controller 14 using the APM message (BICC_APM).
Thereafter, the connection for voice communication between the originating wireless gateway 12 and the terminating wireless gateway 15 is established, using Voice over IP (VoIP) technology, through the core network 13.
The above-described method of controlling relay gateways, in the related art next generation mobile network, adopts the BICC protocol of ITU-T Q.1901. However, the BICC protocol does not include a tone provision function. Furthermore, because the originating gateway controller and the terminating gateway controller may transmit and receive the APM message only once, the transmission of an APM message for the purpose of provisioning a ring back tone is impossible.
Moreover, since the BICC protocol is still in the pre-released state, it is not regarded as a flawless standard. Also, because recommendations on the call processing procedures only concern the ATM based network, it is not yet appropriate to commercialize the VoIP products, in the IP-based network, using the call processing procedures recommended in the BICC protocol.